Department of Agronomy

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Browsing Department of Agronomy by Subject "Alfalfa -- Yields -- Estimates"

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    Direct and indirect methods of estimating lucerne (Medicago sativa) yield
    (Stellenbosch : Stellenbosch University, 2019-12) Makuni, Josiah; Swanepoel, Pieter Andreas; Labuschagne, Johan; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: Lucerne (Medicago sativa) is an important drought tolerant fodder crop which plays an important role in providing feed for livestock in South Africa. Currently, the standard method for determining fodder on offer is the cut-and-dry method, which is time consuming, costly and labour intensive. There is therefore a need to find alternative non-destructive methods that can be used to accurately estimate lucerne yield in a time-efficient manner. The aim of this study was to calibrate a rising plate meter (RPM), ceptometer, meter ruler and canopy cover using an unmanned aerial vehicle (UAV) to estimate lucerne herbage yield. Data was collected from January 2015 till February 2018 with a break from June 2016 to June 2017. The study trial was conducted from July 2017 to February 2018 on existing lucerne trial plots under full irrigation at the Elsenburg Research Farm outside Stellenbosch. The first objective was to determine yield potential of lucerne cultivars available commercially in South Africa. Herbage yield data for 2015 was used to determine yield potential of different cultivars. Dormancy class did not affect herbage production in this study. The second objective was to calibrate indirect methods namely RPM, ceptometer and meter ruler, for estimating lucerne yield. Linear and quadratic regressions were calculated to estimate the accuracy of the RPM, ceptometer and meter ruler. Coefficients of determination derived from three yield estimations were significant (p<0.05). The RPM had the best coefficient of determination of r2 = 0.69 (p<0.05) compared to the other instruments. Operation was fairly easy and it achieved its objective of cutting down on time. It worked best on the months where lucerne production was low. The ceptometer (r2 = 0.55) was highly weather dependent as it worked best on clear sunny days and was affected on days with clouds and morning dew. The meter ruler was quick and easy to use to collect data. However, it could not produce a high coefficient of determination (r2 = 0.50). The third objective was to develop ways to use digital data collected with a UAV for estimating lucerne yield. Linear and quadratic regressions were also calculated to estimate accuracy of the UAV canopy cover. The UAV canopy cover estimations produced the lowest coefficient of determination of r2 = 0.45 compared to the other instruments. The drought experienced in the Western Cape Province during 2017 and part of 2018 cut the data collection period down to seven months from the expected twelve months. For the current study, it was concluded the RPM could be the best yield estimation instrument for estimating yield albeit there is room for it to be calibrated to get higher yield estimation accuracy. It is recommended the study is repeated over a longer period to properly calibrate all yield estimation instruments over all seasons of the year.